Changes in thyroid hormones and free triiodothyronine-to-free thyroxine ratio in euthyroid patients with obesity in terms of different glucose metabolism statuses

Sema Hepsen; Pinar Akhanli; Sencar Muhammed Erkam; Hakan Duger; Hayri Bostan; Muhammed Kizilgul; Arslan Ismail Emre; Erman Cakal

doi:10.1530/endoabs.73.AEP873

Purpose

Thyroid hormones are known to have an essential role in the regulation of energy homeostasis and glucose metabolism. Considering to literature data, variations of thyroid hormones within normal ranges change in obesity and type 2 diabetes mellitus (T2DM) in opposite ways. This study aims to evaluate thyroid hormone levels and fT3/fT4 ratio in different glucose metabolism statuses of euthyroid patients with obesity.

Methods

This retrospective observational study evaluated thyroid hormones and fT3/fT4 ratio of 209 patients with obesity grouped according to their glucose metabolism status.

Results

131 (62.7%), 41 (19.6%), and 37 (17.7%) patients had normal glucose tolerance (NGT), prediabetes, and T2DM, respectively. Serum fT4 level was higher in patients with T2DM compared to patients with NGT (P =0.009), although no difference was observed in TSH and fT3 levels among groups. Baseline characteristics, laboratory test results, and thyroid hormone levels of the subjects are presented in Table 1. FT3/fT4 ratio was determined to be lower in patients with T2DM than patients with NGT (P = 0.012). HbA1c was independently and positively associated with fT4 (β= 0.345, r²=0.119, P = 0.003) and negatively associated with fT3/fT4 ratio (β= –0.371, r²=0.138, P = 0.001).

**Table 1.** Baseline characteristics, laboratory parameters, and thyroid hormones of the subjects
	Patients with NGT (n = 131)	Patients with prediabetes (n = 41)	Patients with DM (n = 37)	P value NGT vs DM	P value NGT vs prediabetes	P value Prediabetes vs DM
Age, years	34 (27–44)	39 (31–46)	48 (38–53)	<0.001	0.045*	0.005
Gender, female, n (%)	105 (80.2)	26 (63.4)	26 (70.3)	0.202	0.029*	0.524
BMI, kg/m²	40 (34–44)	40.4 (33–47)	41.2 (32–49)	0.869	0.676	0.886
FPG, mg/dl	89 (79–95)	104 (98–112)	136 (120–148)	<0.001	<0.001	<0.001
HbA1c, %	5.6 (5.4–5.6)	6.2 (6–6.3)	7.3 (6.8–8.2)	<0.001	<0.001	<0.001
TSH, mIU/l (RR: 0.38–5.33)	2 (1.3–3.1)	2.2 (1.2–3.4)	1.75 (1.3–2.9)	0.398	0.826	0.722
FT4, ng/dl (RR: 0.58–1.6)	0.87 (0.81–0.97)	0.86 (0.81–0.96)	0.94 (0.89–1.1)	0.009	0.769	0.018*
FT3, ng/dl (RR: 2.66–4.37)	3.5 (3.1–3.9)	3.4 (3.2–3.6)	3.4 (3–3.7)	0.054	0.446	0.344
FT3/fT4 ratio	4 (3.5–4.4)	4 (3.4–4.5)	3.6 (2.9–4.3)	0.012	0.967	0.028*

Categorical data were demonstrated with numbers and percentages (%). Other variables were presented as medians (interquartile ranges 25–75).

NGT normal glucose tolerance, DM diabetes mellitus, BMI body mass index, FPG fasting plasma glucose, TSH thyroid-stimulating hormone, fT4 free thyroxine, fT3 free triiodothyronine.

* The P value did not maintain significantly after adjusting according to Bonferroni correction.

Discussion

Serum fT4 level increased and fT3/fT4 ratio decreased in patients with T2DM independently of obesity. The interaction of T2DM with thyroid hormones may overcome obesity-related changes in thyroid functions in our cohort.

Endocrine Abstracts

AEP873